1. Field of the Invention
The present invention relates to sprayable and pourable polyurea elastomers which include novel chain extenders.
2. Description of Background Art
Elastomer systems are commonly recognized as, among other things, coating materials, with spray polyurea elastomer systems being particularly useful when employed in this capacity. One of the considerations confronting the skilled artisan is the sprayability of the elastomer during the critical period, that is, the point at which the reactive components are combined up through the point at which gelation occurs. Similarly, the pourability of the elastomer during the critical period also concerns the skilled artisan where the elastomer is to be poured into an open mold, such as in electric potting type work.
Polyurea elastomer systems are generally prepared by reacting an isocyanate with an active hydrogen component in the presence of a chain extender. Certain known chain extenders react very rapidly with the isocyanate component and, therefore, are not well suited for spray or pour systems, inasmuch as polymerization or gelation occurs so rapidly that the elastomer is virtually unsprayable and unpourable. One of the most widely employed chain extenders is diethyltoluene diamine (DETDA), a product of Ethyl Corporation. Polyurea elastomer systems fabricated from, among other things, DETDA generally exhibit good processing characteristics. However, one of the shortcomings associated with elastomer systems fabricated with DETDA, where sprayable and/or pourability are at issue, is the rapid gelation time. The polyurea elastomer system of the present invention includes a chain extender that reacts slower with the isocyanate component and, accordingly, the rate at which the elastomer will gel is reduced resulting in improved flowability, thereby permitting the elastomer to be sprayed and/or poured. In addition, the polyurea elastomer system of the present invention exhibits certain properties which are similar to or better than those exhibited by systems fabricated from DETDA.
U.S. Pat. No. 3,979,364 describes the use of aminated polyethers as hereinafter used as a component with a polyol to make an elastomer. U.S. Pat. No. 3,666,788 describes the use of cyanoalkylated aminated polyethers in spray systems. The '788 disclosure, in Column 1, states that the aminated polyethers as used hereinafter cannot be used in spray coatings due to very rapid reaction rates with isocyanates.
U.S. Pat. Nos. 4,379,729; 4,444,910 and 4,433,067 describe elastomers which are prepared using a high molecular weight amine terminated polyether, an aromatic diamine chain extender and an aromatic polyisocyanate which may merely be a polyisocyanate or a quasi-prepolymer prepared from a polyol reacted with a polyisocyanate wherein some isocyanate groups are still left unreacted. Various patents have been applied for and received using the basic combination recited above as well as various mold release agents and other additives, such as catalysts and fillers, including glass fibers. For example, see U.S. Pat. No. 4,607,090.
U.S. Pat. No. 3,714,128 describes cyanoalkylated polyoxyalkylene polyamines which are useful for slowing the gelling or hardening of the polyurea component so that good mixing of the isocyanate and amine components can be attained, which gives the sprayed material ample time to adhere and level before gelation of the polyurea coating occurs. This patent does not describe the particular chain extenders employed in the elastomer of the present invention.
U.S. Pat. No. 4,714,778 describes certain alkenylated toluene diamines which are reported as being useful as tri- and tetrafunctional chain extenders for forming polyurethane-urea elastomers.
U.S. Pat. No. 4,816,543 describes a monotertiary-alkyltoluene diamine which is reported as being useful as a chain extending agent for the formation of polyurethane-urea elastomers. At least 50% of the equivalent weight of the chain extending agent is mono-tertiary-butyltoluene diamine.
U.S. Pat. No. 4,806,615 describes reaction injection molded (RIM) elastomers consisting of a cured reaction product of primary or secondary amine terminated polyethers of greater than 1500 molecular weight, an aromatic polyisocyanate, a combination of an unsubstituted aromatic diamine chain extender and a substituted acyclic aliphatic diamine chain extender.
U.S. Pat. No. 4,218,543 describes the use of high molecular weight polyols, certain aromatic diamines and isocyanates for the production of RIM parts. This patent specifically claims as a chain extender 1-methyl-3,5-diethyl-2,4-diaminobenzene (diethyltoluenediamine) and its isomer.
U.S. Pat. No. 4,523,004 discloses a substituted aromatic diamine chain extender in a RIM product.
U.S. Pat. No. 4,631,298 discloses blending various slower reacting chain extenders with diethyltoluene diamine in a RIM system using amine terminated polyethers.
Thus, it is our understanding that a polyurea elastomer system which incorporates the particular chain extenders described hereinbelow and which is sprayable and/or pourable has heretofore been unavailable.